The geometric structure of poly[1-(trimethylsilyl)-1-propyne] was investigated by C-13 and Si-29 NMR spectroscopies. According to C-13 NMR, the geometric structure varied with polymerization catalysts. NbCl5 was inferred to produce more cis-rich polymer than TaCl5. On the other hand, polymerization conditions such as solvent, temperature and cocatalyst hardly affected the geometric structure. The cis contents of polymers bearing bulkier substituents (-SiMe2-nC6H13, -SiMe2-CH2SiMe3) prepared with TaCl5 were similar to that of poly(TMSP) with TaCl5.